The preparation of p-xylylene and functionalized p-xylylene from paracyclophanes is well known, and the subsequent polymerization and copolymerization reactions have been explored extensively over many decades. By far, the most common mode of p-xylylene formation utilizes the Gorham method (U.S. Pat. No. 3,288,728 A). This method typically involves pyrolytic cleavage of paracyclophanes, its functionalized derivatives, or p-xylene to yield p-xylylene di-radicals (M. Szwarc et al., Disc. Faraday Society, 46, 1947), which polymerize to form poly-p-xylylene (also known as parylene) polymers and copolymers. Preparation of bulk p-xylylene, from pyrolysis to deposition, via this route requires low pressure (0.1 to 0.2 Torr) for the entirety of the process. This process is well known to those versed in the field of parylene thin film chemistry.
In early processes by Gorham and Errede (Errede, L. A. and Hoyt, J. M., J. Am. Chem. Soc., 82, 1960, 436-439), pre-formed p-xylylene from the above describe pyrolysis held at sub-zero temperatures (typically −78° C.) under vacuum, was introduced slowly to a heated (>90° C.) secondary monomer, either neat or in a solvent such as hexanes, toluene, or p-xylene, in such a manner that the second monomer was always in excess to the p-xylylene monomer. This encouraged reaction of the highly reactive xylylene monomer with the less reactive secondary monomer. It was only in this fashion that appreciable copolymerization occurred. When xylylene was in excess to the secondary monomer, self-polymerization was the dominant reaction. The reaction was allowed to warm to room temperature, at which point bulk polymer was formed and isolated from the mother liquor.
More recently, chemical vapor deposition (CVD) processes for the formation of xylylene copolymeric thin films have replaced the solution phase bulk polymer syntheses. Morozov et al., Elkasabi et al., and Gaynor et al. (Morozov et al., Pol. Sci. Ser. A, 54, 2012, 330-342; Elkasabi, et al., Adv. Mater., 18, 2006, 1521-1526; Gaynor, et al., J. Mat. Res., 11, 1996, 1842-1850) are among several reports that utilize vacuum vapor deposition of p-xylylene with a number of radical reactive electrophilic monomers including, p-phenylenevinylene, amine and ketone containing [2,2]paracyclophanes, and vinylic monomers (N-phenyl maleimide), respectively.
There existed a need for a simple, rapid, inexpensive method for the formation of xylylene monomers. The process for forming parylene via the “Gorham method” utilizes costly subatmospheric pressure environments and reagents, such as paracyclophanes. To reduce costs associated with producing parylene thin films, the most demanding market for this polymer, the Puralene™ process (Carver, U.S. Pat. No. 8,633,289) was invented. The Puralene™ process converts p-xylene into p-xylylene in the presence of N2O or a reactive oxygen, under atmospheric pressure, and/or without the need of a vacuum. This process is comparatively inexpensive and produces a conformal thin film ranging from nanometers to microns in thickness.
The processing parameters of the Gorham process and related processes are not conducive to adding polymerizable molecules to p-xylylene during formation. Thus, functionally limited p-xylylene products may be formed using such processes.
There is a need for improvements to the p-xylylene polymers. The invention is directed to overcoming one or more of the problems and solving one or more of the needs as set forth above.